Such machine tools generally have a digital control unit, for instance, an NC (Numeric Control) or CNC (Computer Numeric Control) control unit. The control data required for numerical control, such as position and/or path and/or contour data for the desired machining of the workpiece, is fed to the control unit in the form of control inputs and there it is converted into control signals for the servo drive units of the machine tool.
As an example, an EDM machine, that is, an erosive die sinking or cutting machine, could be mentioned. Such EDM machines are used among other things for producing stamps and/or dies of conductive materials. A particularly economical rational use of such EDM machines is the production of molding forms for mass production. This results in the necessity in normal operation of the EDM machine of inputting individual control data, applicable only to the respective workpiece, before machining one or more workpieces. In addition to specifying the desired machining steps, it is also necessary here to take account of possible malfunctions or other exceptional situations during machining, such as a broken wire or a persistent electrical short circuit between the machining electrode and the workpiece of an EDM machine.
In preparing the EDM machine for a work process, that is, in so-called set-up, the machine operator must therefore provide special procedures for the case that such a malfunction occurs. Given the increasing complexity of workpiece machining on modern machine tools, such as three-dimensional erosion with an EDM machine, it is becoming more and more difficult for the machine operator to assess which special procedure or procedures are rational for the specific malfunction at a given point in the machining process. Setting up modern machine tools is therefore becoming more and more complex and elaborate.
Control methods of the type mentioned initially from prior art do not meet these requirements. They require control input in the form of finished "programs," known as control programs. Such a program comprises all control data and specifies, for instance, which cutting paths are to be performed, at what quality, at what point and in what sequence, on the workpiece to be machined. The control data is specified in a sequential series of commands to the control unit of the machine tools. Known control units for machine tools execute such control programs sequentially. The command corresponding to a certain machining step remains active here until a new machining step is specified by a new command in the next step of the command sequence of the control program. Special procedures for possible malfunctions are also provided in this command sequence. These also remain active until a new behavior of the machine tool, a new machining step perhaps, or another special procedure, is specified by a new command in a subsequent line of the command sequence.
The machine operator is left to his own imagination and experience in defining appropriate measures in any exceptional situations. It may be sufficient in die sinking with a simple geometry, for instance, to move away from the workpiece on the fastest possible route, but with a more complex geometry, the same command can lead to damaging the workpiece and/or the machining electrode. A subsequent correction of the control program when an unforeseen exceptional situation occurs also has the disadvantage that the work sequence must be interrupted, a new control program prepared and a new work sequence started.
The present invention aims to improve machine tools, particularly EDM machines, with respect to user-friendliness.